📝 STANDARD DESCRIPTION:
Origin: Branch of vagus nerve, given off in the cranial thorax.
Course (very important — asymmetrical):
- LEFT recurrent laryngeal: Hooks around the arch of the AORTA (longer course).
- RIGHT recurrent laryngeal: Hooks around the right SUBCLAVIAN artery (shorter course).
- Both then run forward in the tracheo-oesophageal groove of the neck.
- End as Caudal Laryngeal Nerve supplying intrinsic muscles of larynx (except cricothyroideus).
Function: Motor to laryngeal muscles that ABDUCT (open) the vocal folds.
Clinical: ROARING (Laryngeal hemiplegia) in HORSES — paralysis of the LEFT recurrent laryngeal → vocal fold falls inward → narrow airway → noisy breathing during exercise.
📚 DETAILED DESCRIPTION:
THE 'U-TURN' NERVE — RECURRENT LARYNGEAL
This branch of the vagus is famous for its strange path. After leaving the vagus in the chest, it loops around a big artery and then turns and runs back UP to the larynx (which is in the neck). That is why it is called 'recurrent' (= going back).
WHY THE TURN? During development, the larynx starts in the chest and migrates forward into the neck, but the nerve loop stays trapped under the artery. So in the adult, the nerve has to take a long detour: down the neck → into chest → loop under artery → back up to larynx.
LEFT vs RIGHT — IMPORTANT:
• Left recurrent laryngeal nerve: Hooks under the aortic arch. Course is long.
• Right recurrent laryngeal nerve: Hooks under the right subclavian artery. Course is shorter.
This left-right asymmetry exists in all mammals.
FUNCTION: Supplies all the intrinsic muscles of the larynx except the cricothyroid (which is supplied by the cranial laryngeal). Most of these muscles open the vocal fold during inspiration. So if this nerve is damaged, the vocal fold cannot be pulled out of the way and partly blocks the airway.
CLINICAL — ROARING (Laryngeal Hemiplegia) IN HORSES:
The LEFT recurrent laryngeal nerve has the longest course of any nerve in the horse. It is very vulnerable to damage. When it stops working:
• The left arytenoid cartilage and vocal fold fall inward.
• During fast exercise, air is sucked over the loose fold → loud whistling/roaring noise.
• Performance drops badly.
Treatment: Surgical 'tieback' (laryngoplasty) to hold the vocal fold open.
Roaring almost always involves the LEFT nerve because of its longer, more vulnerable course. (Easy memory: Left = Long = Loses function.)
// COMPARATIVE ANALYSIS
| HORSE |
Most clinically affected — ROARING is a major performance disease of racehorses. |
| DOG |
Laryngeal paralysis common in old large breeds (Labrador, retriever) — both nerves can be affected. |
| CATTLE |
Rarely affected; roaring is uncommon. |
CLINICAL RELEVANCE
Roaring (Laryngeal Hemiplegia) — HORSE:
• Cause: Idiopathic damage of the LEFT recurrent laryngeal nerve (long course makes it vulnerable).
• Sign: Loud roaring/whistling noise during inspiration when galloping; exercise intolerance.
• Test: Endoscopy shows left vocal fold not abducting.
• Treatment: Laryngoplasty ('tie-back surgery').
